Defrosting control for a refrigeration device



y 1967 R. H. THORNER 3,321,928

DEFROSTING CONTROL FOR A REFRIGERATION DEVICE Original Filed July 19, 1960 2 Sheets-Sheet 1 68b 32b 68a W -J 3 69 INVENTOR. k Qua/527d 7i/o/e/vE/2 BY at A TTOEMFY y 30, 1967 R. H. THORNER 3,321,928

DEFROSTING CONTROL FOR A REFRIGERATION DEVICE Original Filed July l9, 1960 2 Sheets-Sheet.

IN VEN TOR. $0552 Tb. ZQOPMFP ATTOPWFY United States Patent 3 Claims. (Cl. 62140) This is a continuation of Ser. No. 43,825, filed July 19, 1960, and now abandoned which was a continuationin-part of Ser. No. 480,025, filed Jan. 5, 1955, now Patent No. 2,949,016, issued Aug. 16, 1960.

The present invention relates primarily to a control mechanism for refrigeration apparatus and particularly to a control device for controlling the formation and reduction of ice on a cooling unit, such as for defrosting systems of refrigerator apparatus. In a broader aspect, the present invention may be employed to control the thickness of formation of any substantially solid material on (or in) any solid base, such as on a tube, rod, etc.

In numerous refrigerating systems, means are provided to control the build-up and elimination (or reduction) of ice or frost which may form on the evaporator. These systems often include heating means to remove or reduce such formation of ice. In certain types of commercial refrigeration such as ice-bank systems, as well as in some defrosting systems, such removal means comprises merely a switch to turn the compressor off so that the ambient heat eventually diminishes the ice coating on the evaporator. For purposes of this disclosure, ice and frost can be considered synonymously.

Defrosting control systems are used to remove the frost which forms on the usual evaporator coils as well as on other parts or on food adjacent thereto in a refrigerator. Such frost is highly undesirable since it acts as an insulator for the normal extraction of heat from the food compartments to the cooling unit thereby reducing the efficiency thereof. Accordingly it is desirable to remove the frost quickly without melting the food, ice cubes, etc. Hence it has been rather common practice to provide additional means to intermittently apply heat to the evaporator and adjacent parts to periodically remove such frost rapidly and automatically. Such defrosting means usually comprise a separate electric heater element adjacent the evaporator coil or a solenoid-operated valve which acts to pass the compressed refrigerant (such as Freon) directly from the compressor to the evaporator while bypassing the condenser and capillary tube of the refrigerant circuit. The present invention is concerned in the forms shown, with the means to control the thickness of formation of ice or frost on the surface of any of the refrigeration systems above referred to. The present invention is more specifically concerned, by way of eX- ample, with control means for initiating and terminating the intermittent action of the defrosting means of a refrigeration system.

The presently known defroster control devices provide manual or automatic means to initiate the defrosting action. The manual means usually comprises a push button so that initiation depends upon human decision. The presently used automatic initiating means frequently comprises a clock mechanism to start the defrosting action after a definite time interval, such as twenty-four hours, or after a predetermined total running time of the compressor, such as twelve hours, for example. All present defroster control devices provide automatic means to control the duration (or termination) of the defrosting action. Such terminating means usually comprises a gasfilled bellows-type thermostat to shut off the defroster action when the temperature in the controlled food compartment rises to a predetermined value. However, sometimes clock mechanisms are also used to control duration.

A novel means for terminating the defrosting action which senses ice formation is disclosed in the abovereferred to patent, and the present invention relates to improvements in the invention therein claimed.

Defroster control devices in recent years have become widely used in domestic refrigerators having a food freezer section that is separate from the so-called refrigerator or fresh food section. The freezer section in such refrigerators is provided with a fan to circulate air over the evaporator coil and the frozen food products. With this construction and with intermittent defrosting of the freezer evaporator, frost never forms on the food, and melted frost from the evaporator coil is disposed of automatically.

It has always been important to terminate the defrosting action as soon as all of the frost melts in order to prevent unnecessary heating of the food compartments and possible melting of frozen foods therein. However the initiation of the defrosting action has not been too critical in refrigerators that lower the temperature only slightly below freezing, such as to 2528 F., as in the fresh food compartment. But when defrosting the freezer sections of refrigerators having two food compartments, control of initiation is somewhat more critical. This is true since near-zero degree temperatures are maintained in the freezer section to assure rapid freezing of foods placed therein, and to assure that the desired freezing is not hampered by insulation produced by excessive formation of frost. This problem is even more severe because of the loss in efliciency caused by transferring heat twice; the heat first is transferred from the food to the circulating air, and secondly from this air to the evaporator.

Neither the initiation nor termination of a defrosting cycle, if correct, should be a function of time alone. Much worse, clock mechanisms not only are complex and costly but are very unreliable and are likely to become so noisy as to require replacement.

For termination of the defrosting cycle, gas filled bellows which sense only temperature are not only costly, but the gas therein is adversely affected by variations in air density. Accordingly, altitude or air density compensation means frequently are provided to compensate for the low atmospheric pressures such as normally exist at Denver, Colorado, for example.

It should be appreciated, of course, that the melting of frost or frozen food is not only a function of temperature of the surrounding materials but a function of time as well. Frozen foods or frost will melt in a short time at high ambient temperature, but can withstand ambient temperatures of a few degrees above freezing for a relatively long time Without deterioration. It has been found that some of the present defroster controls which sense only temperature act to turn off the frost-destroying heating element too soon if the frost formation is heavy and if the calibration has been established on the basis of a light frost accumulation.

In those applications in which the controlled material is fragile or friable, such as frost, the past attempts to mechanically sense the thickness of such friable material (frost) have required that the sensing member applies a force against the material (frost in the examples herein) which tends to crush or deform the surface thereof; this action, in turn, tends to produce inaccurate or inconsistent results.

Secondly, in some of the past attempts to mechanically sense the thickness or amount of material forming on a base, as above discussed, the control means (which usually includes means such as an electric switch) is moved gradually as a function of the formation of the material. In this instance, the operation of the electric switch is critical since the snap action must be set carefully to correspond exactly to the correct thickness of material.

A broad object of the present invention is to provide a simple and novel mechanism to control the amount or thickness of formation of any substantially firm or solid material on any .solid base.

Another object of the present invention is to provide a mechanism to control the amount or thickness of formation of any material on a surface or base as described in the preceding paragraph, in which a periodically movable member is provided to sense the material formation with a force that will not deform the material to produce erratic measurement thereof, which sensing force monitors a separate and larger force to actuate the control means in a servo-mechanism action.

A further object of the present invention is to provide a mechanism to control the amount or thickness of formation of any material on a surface or base, as described in either of the preceding two paragraphs, in which the control means is operated only after the material forms to substantially the desired predetermined amount or thickness.

A most important object of the present invention is to provide a mechanism to control the amount or thickness of any material on a surface or base as described in any of the preceding paragraphs in which means are provided to produce a relatively small amount of energy, and integrating means are provided to store the energy over a period of time to be released periodically for providing the large amplified force for actuating the control means.

A primary object of the present invention is to provide in an automatic defroster control device simple, inexpensive, quiet, trouble-free and consistent fluid-operated means to effect initiation of a defrosting system by a direct measurement of the thickness of the frost formation.

Another object of the present invention is to provide an automatic defroster control for a refrigerator having fluid operated means to initiate the defrosting action as a function of the thickness of frost formation, and having means to terminate the defrosting action which is dependent on the melting of a specific "body of ice.

A further object of the present invention is to provide in an automatic defroster control system novel means to control the duration (and termination) of the defrosting action including a sensing member immersed in a vessel in the flow path of melted frost and including means to initiate the defrosting action when first starting the refrigerator after installation and before the ice-containing vesse-l is filled with water.

Other objects and advantages of the invention will become apparent from the following description and from the accompanying drawings, in which:

FIG. 1 is a somewhat diagrammatic illustration of a refrigerator having a freezer section with the device of the present invention shown in its operative relation to the several components of the refrigerator;

FIG. 2 is an elevational view of a device (with its cover removed) for controlling the duration of the defrosting action and for terminating same;

FIGS. 3 and 3a show somewhat diagrammatic partial sectional views of one form of the control device of the present invention in which the source of fluid pressure for initiating the defrosting action is produced by opening or closing of the refrigerator door;

FIG. 4 is a sectional view along the line 44 of FIG. 3 showing my improved ice sensing means for terminating the defroster action;

FIGS. 5 and 6 are fragmentary views of the device of FIG. 3 illustrating modified means to sense the formation of frost;

FIG. 7 is a diagrammatic view of a modified power means using a source of energy for initiating the defroster control in response to changes of pressure of the re frigerant:

FIGS. 8, 9, 10 and 10a are somewhat diagrammatic partial sectional views of other forms of the initiating system of the present invention in which the force for initiating the periodic defrosting action is produced by means energized by electro-magnetic or thermal means;

FIG. 11 is a diagrammatic view of a modified form of the invention showing novel energy integrating means to provide periodic large forces for initiating the defrosting action with a relatively small energy source, and,

FIG. 11a is a diagrammatic view, with parts in section, of a modified form of electromagnetic initiating means.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phr-aseology or termnology employed herein is for the purpose of description and not of limitation.

In a broader aspect of the inventive concept, I provide a control device to effect a change in condition, such as bulk or thickness, of any firm or solid material such as frost for example. I provide control means for regulating the change, such as a switch in an electric circuit, and actuating means normally movable independent of the control means and disposed to operate same periodically. I provide sensing means mounted at a predetermined relationship with respect to the material and movable in relation thereto (intermittently) in response to the periodic movements of the actuating means. The sensing means is disposed to prevent the actuating means from operating the control means whenever the intermittent movements of the sensing means is not blocked or prevented by the bulk or mass of the material; but whenever the intermittent movements of the sensing means is blocked or prevented by the bulk of the material, the actuating means can then operate the control means.

In addition, the foregoing combination may be arranged for those application in which the material is friable or fragile (such as frost), to provide that the force of the movable sensing element acting on the friable material is substantially less than the force of the actuating means for operating the control means; so that the force of the sensing means does not crush or deform the material to cause inaccurate or inconsistent results. In this action, the control device provides an action similar to any fluid or electric servomech-anism.

In accordance with the specific form of the invention as shown herein, I provide an automatic defroster control for a refrigeration machine in which the detrimental factors of present controls such as high cost, complexity, excessive noise, unreliability, inconsistency, and variations with air density are eliminated, and which will initiate the defrosting action after a predetermined thickness of' frost is formed, and will melt substantially all the frost (without melting the frozen foods) and then terminate the defrosting action. I provide such desirable initiating action by utilizing a fluid (pneumatic) system or circuit using air as a medium in which the actuating means includes a pressure responsive member disposed to initiate the defrosting action and to actuate or set the means to control the duration of the defrosting action. I further provide in one form of my invention valve means for closing said fluid system, which comprises the sensing element of the sensing means. The valve means is mounted a predetermined distance from a portion of the evaporator such that progressive formation of frost gradually reduces the possible degree of valve opening. I also provide a source of energy which is converted to fluid pressure energy in the fluid system which will periodically provide a pressure to activate the pressure responsive member only when the valve means is unable to open sufficiently to relieve such pressure by reason of the formation of a predetermined thickness of frost. In one form of the invention the source of -fluid pressure comprises a pressure producing member energized by the opening and closing of the refrigerator door. In other forms of my invention, I provide various other energy means as a source to provide forces for actuating the pressure producing member which means are dependent on the cycling of the compressor in some forms of the invention illustrated herein; such energy means may include a heating element for a temperature responsive bimetal, or a heated gas-filled bellows, or a solenoid, arranged to provide relatively quick movements of the pressure-producing member. This source-energy is converted to another form of energy, such as pressure energy, to perform the defrost-controlling action above described. Although any means for controlling the duration of the defrosting cycle may be used and operated by the above- =described initiating means, I have disclosed herein a novel means dependent on the melting of ice in a vessel located in the flow path of melting frost (or in other such container adjacent the cooling unit) to control this duration, which novel means has especial utility when used in combination with my novel cycle initiating means.

In an important sub-combination invention, I provide a relatively small source of such energy or power force to operate an integrating mechanism which stores or adds up this small energy over a period of time and releases the stored energy periodically at a force substantially larger than the original power force.

Referring now to the drawings, and particularly FIG. 1, there is shown diagrammatically by way of example an installation of the present invention as a defroster control unit in operative relation to a refrigeration machine and the electric circuits necessary for operation of the control unit. The entire defroster control may be considered to comprise two components. A control unit 15 which controls the duration (or termination) of the defrosting action, as shown detailed in FIG. 2, is the first component; and the initiating mechanism or means, a portion of which comprises a housing 17, is the second component. In FIG. 1, a typical refrigerator is illustrated having a cabinet (in dotted outline) forming a food freezer section 19 and a fresh food section 21 divided by walls 23 and 25. The refrigerant system includes the usual compressor C which sends the refrigerant through a tube 27 to a condenser D, thence through a capillary tube 29, to be expanded through a frozen food evaporator or cooling unit 30, Where it either returns under vacuum to the compressor through tube 31 or flows to a second evaporator 30a (shown dotted) for the fresh food section 21, all in a manner well known to those skilled in the art. A conventional solenoid-controlled valve S is mounted in a tube 32 which may bypass refrigerant around the condenser directly from the compressor to the evaporator coil 30. When the solenoid valve is opened, by action of the defroster control to be described, the hot refrigerant passes directly from the compressor through the evaporator which quickly melts all the frost formed thereon. The melted frost drops into a trough 34 mounted at the back of the freezer section where the water flows through a tube 36 to a pan 38, where the heat of the condenser helps the melted frost to evaporate. In normal operation, the contents of the freezer section are cooled by air circulated by a small air fan (not shown) which causes air to circulate around the freezer section and over the evaporator 30 and frozen food.

Temporarily referring to FIG. 2, to be discussed in detail hereinafter, the unit 15 includes an electric switch having a fixed contact 39 connected to a terminal 40, and an opposed fixed contact 42 connected to a terminal 44. A movable contact 46 is carried by an arm 48 swingable about a knife edge connection with a support 50 and is connected to a stationary terminal 52. A strong extension spring 53 is connected at one end to the contact arm 48 and at its other end to an arm 54. The switch is shown in its normal position without the defrosting system in operation, and in this position terminal 52 is electrically connected to terminal 40 through contact 46 resting on contact 39 by the force of spring 535. When arm 54 is moved to the dotted position 54 by means to be described, spring 53 is moved over center to the right, as viewed in FIG. 2, so that contact 46 snaps against contact 42 to electrically disconnect terminal 52 from terminal 40 and connect to terminal 44. In this position, however, the spring 53 maintains a relatively large force urging the arm 54 back to the full line position shown in the drawings since the position of the spring is: always at the left of the fulcrum of the arm '54. When arm 54 is moved back to its original position shown, the contact 46 is snapped back to its original position shown in FIG. 2.

Again referring to FIG. 1, line voltage is directed through a wire 56 to a two pole thermostat switch 58 for the freezer section which energizes compressor C when the temperature at a bulb 60 rises to a predetermined value. Line voltage from wire 56 also is taken to terminal 52 of the defroster control unit 15. Another conductor 62 connects the normally closed pole of switch 58 to terminal 44 (FIG. 2). Also the solenoid valve S is connected to terminal 44 by wire 64 in parallel with the compressor when the circuit to the latter is closed only through the switch in unit 15.

The action of the refrigerator and defroster control is as follows. When thermostat switch 58 closes the left pole as viewed in FIG. 1, with the switch of unit 15 in the position shown in FIG. 2, the compressor lowers the freezer temperature in a normal manner until shut off by the thermostat. However, when the defroster control causes arm 54 to move to position 54' in a manner to be described, the compressor C is operated regardless of the position of switch 58, and solenoid valve S opens the bypass line 32 to pass hot gas through the evaporator 30 until all the frost melts and is collected in pan 38 as described. After all the frost is melted, the defroster control causes arm 54 and contact 46 to return to the position shown in FIG. 2, by means to be described.

It should be appreciated that there are many possible combinations of refrigerator arrangements and circuits. For example a refrigerator may have one or two separately closed compartments; in a two compartment unit, the freezer section may be on top or below; or the defrosting system may utilize hot gas or electrical resistance units, etc. Also, the defroster control 15, 17 might be mounted in many different portions of the refrigerator, such as the back of the freezer section between the inner or outer liner, or mounted inside the freezer compartment directly on the coil 30. In addition, the icethickness or defroster control device can. be used for any kind of refrigerating machine, not just as a defroster control for the freezer section of a domestic refrigerator as described in connection with the principal form of the invention. Hence, the particular combination shown in FIG. 1 is merely illustrative, in which the defroster control is shown mounted between the inner liners 23 and 25 which separate compartments 19 and 21, for controlling the frost in the freezer section 19 shown in the lower portion of a two compartment domestic refrigerator.

Now referring to FIGS. 2-4, the means to control the duration (hence the termination) of the defrosting action will now be explained. In unit 15, the mechanism is encased in a housing 68 of any suitable material such as sheet metal with three sides 68a folded up from the base.

A fourth side is formed by the electrical insulating base 69 for the switch, which base has a plurality of projections 69a for insertion into holes in the sheet metal housing and cover to be secured together by upsetting portions of the sheet metal. The housing 68 includes projections or tabs 68b cooperating with suitable openings in a cover 70 (FIG. 3) to be staked or bent to secure the cover to the housing. In unit 15, arm 54 carries a detent member 72 hinged thereto at one end to permit angular movements of the detent in relation to arm 54. A light extension spring 74 is suitably secured at one end to arm 54 and at its other end to detent 72 urging the detent downwardly into engagement with a cam or guide member 76 which is secured to one side of housing 68 by suitable means as by staking or soldering.

A bushing member 78 includes a hexagonal flange which is secured to the inside of housing 68 by suitable means as by soldering or staking. The bushings 78 includes a bore to journal a shaft 80 which carries a latch member 82 secured thereto for angular movements with the shaft. A very light extension spring 84 is suitably secured at one end to housing 68 and at its other end to a portion 82b of latch member 82 to urge same in a counterclockwise direction into the free position shown in FIG. 2. Detent 72 includes a catch portion 86 disposed to engage a latch arm 82a of latch member 82 in a manner to be described. A rectangular shaft 90 is supported and guided by a tab 92 (struck inwardly from housing 68) for axial sliding movements to abut and actuate arm 54 as shown.

In FIG. 3, unit is shown with its cover 70' installed and the unit mounted in its operative position between inner walls 23 and 25 of chambers 19' and 21, respectively. Shaft 80 projects outwardly through cover 70 (perpendicular to the drawing) and has a sensing arm 94 secured thereto by suitable means, as by a set screw, for angular movements therewith. A small vessel 96, as shown in FIGS. 3 and 4, is suitably secured to a portion of the evaporator tubing such that the vessel is below the tubing. The vessel may be made of any suitable material, but a metal such as aluminum is desirable to provide the highest heat conductivity which is facilitated by wrapping a portion 96a of the vessel around the tube. The vessel is mounted so that an offset sensing portion 94a of arm 94 is suspended inside an ice chamber 98 formed by the vessel. A light leaf spring member 160 may be secured to arm 94, as by rivets, and is slightly pre-bent to ride against the surface of portion 96a in operative movements of arm 94 for reasons to be discussed.

The operation of the defrosting duration or termination control unit above described is as follows. Referring to FTGS. 14, assume that chamber 98 of vessel 96 is completely filled with water or other freezable liquid which is frozen in normal refrigerator operation. After frost forms on the evaporator to a predetermined thick ness or depth, shaft 90' is automatically moved temporarily to the left by means to be described until arm 54 is moved to the position at 54'. This action causes contact 46 to move against contact 42 which operates the compressor and solenoid valve to send hot gas through evaporator 30 for melting and disposing of the frost in a manner previously described. At this time the ice or frozen liquid in vessel 96 is also subjected to heat somewhat by radiation but primarily by conduction from the tube 38, which is the reason why a vessel made of a metal of high heat conductivity may be desirable. Also, movement of the switch arm to the position at 54 carries detent 72 leftward until spring 74 causes catch portion 86 to engage latch arm 82a. The force on shaft 90 is soon removed, as will be described. Then the force of spring 53 tends to return arm 54 into the position shown with a force that easily overpowers the force of spring 84. Such forces are transmitted through detent 72 which now abuts latch arm 82a tending to impart angular movement to latch member 82. However, such angular movements are prevented by arm 94 now abutting against the ice or frozen liquid in vessel 96 which tends to be compressed between the left edge of the sensing portion 94a and the left inside wall 96b of the vessel. Thus, the ice acts as an ice or frozen-liquid link which grows smaller gradually as the ice or frozen-liquid progressively melts since contact with the melting ice is maintained by spring 53. As arm 54 with its detent member 72 gradually moves rightwardly when the ice in vessel 96 melts, a cam portion 72a of the detent member contacts cam 76 which gradually raises the detent member in opposition to spring 74. After a predetermined travel of arm 54 and detent 72 which is calibrated to occur when all the frost is melted, the catch portion '86 disengages from latch arm 82a. This instantly causes two simultaneous actions as follows: The first action is that spring 84 instantly returns latch member 82 into the angular position shown in FIG. 2 in which arm 82b contacts the lower side of the housing; accordingly the sensing portion 94a is moved rightwardly away from the remaining ice and restored to the position shown. The second simultaneous action is that spring 53 causes arm 54 and detent 72 to snap into the position shown in FIG. 2, which also moves the contact 46 into the position shown against contact 39. This terminating action causes the solenoid valve S to shut off the flow of hot gas through the bypass tube 3 2 so that refrigerator operation is again normal. The compressor is again controlled only by thermostat 58, and the ice in the vessel 96 soon freezes so that the defrosting cycle can be repeated as above described after a predetermined thickness of frost is formed.

It is important to appreciate that all the ice in vessel 96 may not melt, but only that portion adjacent the metal surfaces such as at sensor portion 94a and the interior walls of vessel 96. The unit 15 is so calibrated that when all the frost on the evaporator is melted, the detent member 72 is disengaged from latch arm 82a after a predetermined travel. This can be controlled by numerous variables such as the height of chamber 98, the thickness of metal of sensing portion 94a, the vertical adjustment position of cam 76, etc.

It is important to appreciate that the detent travel is always larger than '(and easily includes) the travel necessary to cause contact point 46 to snap between contacts 39 and 42. Hence, the production setting of the switch snap is not in the least critical, as in many prior devices; because for production units it is only necessary to provide the relatively large travel of detent 72, such as by setting the vertical position of release cam 76.

When the refrigerator is first placed in service, the present invention provides novel means so that it is unnecessary to fill chamber 98 with water initially to make the defrosting system operative. The construction also produces a more accurate calibration since the device is arranged to sense the accumulation of frost directly. As explained above, an abutting frost sensor such as leaf spring 106, contacts either tube 36 or vessel portion 96a in all positions of arm 94. Also, vessel 96 is mounted below tube 30 to be in the flow path of melting frost to keep chamber 98 completely filled, whereas the overflow falls into trough 34 to be evaporated as described. As explained above, the control is calibrated to terminate the defrosting action after a predetermined melting time dependent on numerous factors including a completely full amount of water in vessel 96. Thus, as calibrated, if chamber 98 is only one-half full, the defrosting action would terminate before all the frost is melted.

The defrosting action is developed as follows, starting with a completely empty vessel at the time the refrigerator is first placed in service. When the frost forms to its predetermined thickness on tube 30 (FIG. 4), a portion of the frost covers the frost sensor leaf spring 100. Then when shaft is moved to start the first defrost heating action, arm 94 is moved gradually to the left by spring 53 as the frost which is abutted by leaf spring 100 melts until detent 72 disengages from latch arm 82a. The frost tends to be compressed between the leaf spring 100 and stop means, such as a tab 960 (FIG. 3) which projects transverse to the tube. In other words,

the leaf spring 100 actually abuts the frost trapped between the spring and the tab 96c. However, without water in the vessel (as calibrated), only a small portion of the frost melts on this first cycle but some of this melted frost falls into chamber 96 to cover perhaps only the end of sensor portion 94a. Then the second defrosting cycle will be longer due to the small amount of ice added in vessel 96, so that a larger percentage of the frost is melted during this second cycle. Some of the additional melted frost again falls in chamber 98, so that a higher percentage of frost is melted on each subsequent defrosting cycle. This action continues until the vessel 96 is completely full so that all the frost is melted during eachsubsequent cycle as calibrated. In actual operation, the vessel is full after only the first few cycles when the refrigerator is first placed in service. The leaf spring 100 might be omitted if arm 94 were mounted close enough to be embedded in the frost that forms on tube 30. However to accommodate production variations, the leaf spring 100, or equivalent, is provided. In any case, the calibration is partly produced by the arm 94 or leaf spring 100 compressing or abutting the frost between it and tab 96c and partly by the sensing portion 94a compressing or abutting ice between it and the wall 96b of the collecting vessel.

Tests of this concept have shown that the defroster control can be calibrated satisfactorily to terminate the defrosting action without vessel 96 by using only the direct frost sensor (leaf spring 100) or equivalent abut ting means as a sensing member to entrap frost between the sensor and projection 96c or equivalent stop means. However in this instance, the control device must be mounted on the evaporator coil 30 somewhat near the last portion of frost to melt. When the vessel 96 is combined with the abutting frost-sensor 100, although the cost increases slightly, the control unit can be mounted anywhere on the evaporator coil since the travel of sensor arm 94 can be calibrated to terminate the defrosting action at a position corresponding to the last portion of frost to melt, even if remote from the control device.

The principle of the duration control unit 15 as above described, except for the automatic vessel-filling means shown in FIG. 4, is disclosed in Patent No. 2,949,016, in which the theoretical concepts are discussed in more detail. It is important to appreciate that any duration (termination) control device may be used or operated by the novel initiating control means now to be described. However, the inherent simplicity, reliability, consistency, function accuracy, and potentially low cost of the duration control disclosed herein provides an inventive combination with the initiating means now to be described.

Now consider the means to initiate operation of the duration control device, which in the specific duration device disclosed herein, comprises the means to effect periodic or intermittent movement of shaft 90 after a predetermined amounf of frost has formed. Referring to FIGS. 3 and 3a, shaft 90 is actuated by a pressure responsive member 102 such as a single or multiple fold flexible diaphragm made of any suitable material either metallic or non-metallic such as synthetic rubber. The diaphragm is operated by air as a working medium and is secured between housing 17 and a cover 104 to form two air chambers 106 and 108. Chamber 106 is vented to the atmosphere through holes 110, While chamber 108 communicates with any source of air pressure, to be discussed, through a conduit, tube, or passage 112, which actually is a part of chamber 108 from a fluidic standpoint. A tube or passage 114 connects with passage 112 and projects through wall 23 into the freezer compartment as shown. A valve 116 normally closes the end of passage 114, and a very light leaf spring 118 is pre-bent to support and maintain valve 116 in its closed position. Leaf spring 118 is secured at one end to a fixed portion of the refrigerator, such as to a post I frost forms on the evaporator tube 30 to 120, to enable swingable valve movements as leaf spring 118 bends to open valve 116 as will be discussed. Tube 114 is mounted in relation to the evaporator tube 30 such that leaf spring 118 and valve 116 is positioned a predetermined distance T from evaporator tube 30, so that these elements comprise the frost-sensing portion of the invention. Passages 112 and 114 may include, in one form of my invention, another passage 122 having an inlet check valve 124 biased closed by a hair-spring 126. It is important to appreciate that any other kind of valve construction, such as a simple ball valve, may be used in place of valve 116 and leaf spring 118 as long as its movement can be limited by the formation of frost as explained.

Energy-responsive means are disclosed to produce a periodic source of air pressure to passages 112, 114 and 122, which means may comprise some type of pumping apparatus. In the form of the invention shown in FIG. 3:: such pressure-producing means comprise another diaphragm assembly 128 mounted remotely from diaphragm 102 and located anywhere between the inner liner 130 and outer liner 1.32 to be adjacent the door 134 of the freezer compartment. The assembly 128 includes a diaphragm 136 preferably of synthetic rubber, although a metallic or synthetic rubber bellows might be used. Diaphragm 136 is secured between a housing 138 and a cover 140 which forms two air chambers 142 and 144. The cover 140 is secured to a wall 143 of the refrigerator by any suitable means. Chamber 142 is vented to the atmosphere by holes 146, and chamber 144 communicates only with passage 112, such as by a long metal or synthetic rubber tube strung between the inner and outer walls of the refrigerator. A shaft 148 is guided by a bushing 150 and is secured to diaphragm 136 and biased by a spring 152 to abut door 134 when closed as shown. The passages 112, 114, 122 and chambers 108 and 144 comprise a fluid (air) circuit, which circuit in the form of the invention shown in FIGS. 3-3a would include the sensing valve means 116, 118 and intake valve means 124, 126 and may also include, or at least be associated with, diaphragms 102 and i136 which comprise movable walls for chambers 108 and 144, respectively.

The operation of the entire initiating system is as follows. When the door 134 is opened, spring 152 forces diaphragm 136 to its extreme rightward position which draws air through inlet check valve 124 (valve 116 being closed) through passages 114 and 112 into chamber 144. When the door is again closed it moves the shaft 148 and diaphragm 136 quickly to its normal leftward position as shown. This action causes the intake air to be forced out at a very low pressure through valve 116 (valve 124 now being closed) which is free to open providing it is not blocked by frost on tube 30. Hence in this action, the air pressure does not build up sufliciently in tube 112 and chamber 108 to actuate diaphragm 102 in opposition to the force of spring 53 (FIG. 2), so that at this time valve 116 acts as a relief valve. However, after a predetermined thickness T at or near the leaf spring valve 116 the valve is blocked from normal opening by the frost. Then after the door is opened and air drawn into the system, a subsequent closure of the door causes air pressure to build up in the air circuit passages and chambers 114, 122, 112, 144 and 108 to force diaphragm 102 and shaft 90 to the left, as viewed in FIGS. 2 and 3, which moves arm 54 to the position 54' to initiate the defrosting action as above described. After the duration unit 15 terminates the defrosting action when detent 72 disengages from latch arm 82a as already explained, spring 53 causes arm 54, detent 72, shaft 90, and diaphragm 102 to snap into the position shown; and since the frost is then melted from tube 30, the air from chamber 108 is easily forced out through valve 116 by diaphragm 102, so that the entire cycle can be repeated.

Since frost is fragile and friable, only a very slight force can be applied thereon to sense its thickness with acceptable consistency and accuracy. As above discussed, the force and travel of the sensing element in my invention can be very small compared to the force and travel of the actuating member; and this small sensing force and travel controls the larger separate force and travel. Thus the action is similar to a fluid or electric servo-mechanism. In this action the frost-sensing element such as the sensor 116 applies a very small force acting periodically on the frost to control the transmission of a relatively large and separate actuating force, as produced by diaphragm 136, to an actuated member, such as shaft 90, for operating the control switch.

FIG. shows a modified form of the frost-sensing portion of the invention in which the end of tube 114 itself is positioned a predetermined distance T from the evaporator tube 30 without any valve means at its end. With this construction, which could be used with any direct measuring ice-sensing device, frost must build up at least to thickness T to cover the end of tube 114 before the control unit 15 can be operated. Then when door 134 is closed, pressure builds up in chamber 1108 to move diaphragm 102, shaft 90, and arm 54 which actuates unit 15 as above described.

FIG. 6 shows still another modified form of the frostsensing portion of the invention in which the passage 122 and check valve 124 could be omitted. Instead of the check valve 124 a very small bleed orifice 154 is provided in a wall of tube 114, which could also comprise a small notch on the seat for valve 116. Then when the door opens, air is slowly drawn into chamber 144 by spring 152 acting on diaphragm 136. When the door closes (with frost formed on tube 30), the pressure builds up rapidly and sufficiently in passages or chambers 112, 114, 144 and 108 to actuate diaphragm 102 which initiates unit 15, since the air cannot escape fast enough through the small bleed orifice 154. In FIG. -6, another modification of the frost-sensing means is illustrated which includes an extension 116a for the valve 116. In this construction, the valve 116 is positioned farther above tube 30 so that its extension 116a is set a predetermined distance T above the tube 30 (when valve 116 is normally closed). The advantage of this construction is that the periodic air bleed through valve 116 will not prevent normal formation of frost on tube 30; and, also, no frost can form at the valve itself.

In the forms of the invention shown in FIGS. 3, 3a, 5 and 6, the defrosting action is initiated by the first normal 'door'opening following the build up of frost to a prede termined thickness T. The forms of the invention disclosed in FIGS. 7-1111 utilize energy associated with the normal cycling of the compressor to provide a periodic source of fluid pressure. In these forms of my invention the defrosting action is started at a compressor cycle following the buildup of frost to the predetermined thickness T. In the form of the invention in which the valve :116 senses the formation of frost, it is necessary that the pressure is produced only periodically in the air circuit 108, 112, 114 and 144. This is desirable so that the valve 116 can be normally closed while frost forms, and moves against the frost only occasionally to feel the same, thereby sensing its thickness. If the valve were held open continuously, for example by a continuous supply of pressure in the air circuit, the frost might form around the valve and hence it would not be able to sense the frost thickness, which must be done by periodic excursions of the valve against the frost while it forms.

FIG. 7 shows a modification of a portion of FIGS. 1 and 3, 3a, in which like elements bear like reference numerals. In FIG. 7, the vacuum tube 31 communicates with a sealed chamber 156 of a bellows 158. Thus when the compressor starts, vacuum is produced in tube 311 and chamber 156 causing bellows 158 to contract. This action causes the diaphragm 136, which is secured to the free end of bellows 158, to compress air in chamber 144 the pressure of which is transmitted to chamber 108 through passage 112 to activate unit 15 as before when sufficient frost is formed on tube 30. The pressure portion of the refrigerant circuit could be used instead of vacuum by rearranging the bellows and diaphragms without changing the scope of this concept.

FIG. 8 shows another modification of FIGS. 1 and 3, 3a, in which like elements are indicated by like reference numerals. In FIG. 8, the diaphragms 162 and 136 are clamped to a central housing 166 by the housing or cover 17 and a spacer 162, respectively, to form a chamber 164 that corresponds pneumatically to passages and chambers 108, 112 and 144 in FIGS. 3, 3a. A snap-action bimetal member, such as a bimetal disk 166, is held in a circular groove formed in spacer 162 and a cover 168. The disk 166 is connected to actuate diaphragm 136 through a shaft 170. The cover 168 forms a chamber 172 which includes an electric resistance heating element 174 and insulating liners 176 for heating the bimetal disk. The electric circuit may be modified from that in FIG. 1 with the addition of heater 174 energized through a wire 175, and the system operates as follows. When thermostat 58 is off, the compressor C, heater 174, and solenoid valve are all deenergized. When the thermostat switch 58 closes in normal operation, the compressor starts and heater 174 is energized. The heat energy produced by element 174 causes the disk 166 and diaphragm 136 to snap to their most leftward positions for the purpose of converting heat enermgy to pressure energy. As described previously, without frost on tube 30, valve 116 opens at a low pressure energy to prevent sufiicient pressure buildup for actuating diaphragm 102 and unit 15. But on the first compressor actuation following the formation of frost to a thickness T, pressure energy is built up by the disk snap-action to actuate diaphragm 102 and initiate unit 15. Then with arm 54 in the position 54, the compressor continues to run and solenoid valve S sends hot gas through the evaporator as described above. When all the frost has melted, the arm 54, shaft and diaphragm 102 snap back into the positions shown regardless of the position of the disk, since air can now be exhausted through valve 116. For this form of the invention, it is desirable to provide a snap-action to diaphgarm 136 so that the pressure energy will build up in chamber 164, even though valve 116 might leak slightly, or if orifice 154 is use-d. Any conventional bimetal snap-action element may be used, such as a cantilever type bimetal member, to actuate diaphragm 136, so that the disk type of snap action element 166 is merely shown by way of illustration.

FIG. 9 shows a modification of the form of my invention shown in FIG. 8 except that the heater and bimetal disk is replaced by a solenoid. Also, by way of illustration, an electric heater type defrosting system is shown in place of the solenoid valve to bypass hot gas as in FIGS. 1, 8 and 11. It is important to appreciate that any of the defrosting systems and electric circuits may be operated by any form of my control invention disclosed herein, as well as other commonly used circuits not discussed. In FIG. 9, elements common to those in FIGS. 1, 2, 3, 3a and 8 are indicated by the like reference numerals. Diaphragm 136 is clamped between spacer and a cover 178 to which an electro-magnet or solenoid 180 is secured by suitable means. The solenoid comprises a coil 182 and an armature 184 operatively connected to diaphragm 136, as by a shaft, to effect movement thereof. A spring 186 is mounted in chamber 164 and retained by an abutment 188 to act on diaphragm 136 to oppose the force of armature 144. The electric circuit is slightly modified so that the compressor and solenoid 180 are off when thermostat switch 58 is open, and a defroster heater 190 is also off since it is connected to the normally open terminal 44. When the thermostat switch 58 closes, the compressor and solenoid 180 are energized so that armature 184 moves diaphragm 136 quickly to the left. This action has no effect on diaphragm 102 and unit 15 if no frost is formed on tube 30. However, when frost forms on tube 30 to a thickness T, the next closure of switch 58 causes unit 15 to be activated in a manner described above to start the defrosting action. At this time the compressor is turned off while the heater 190 is energized to melt the frost, which is terminated by unit 15 as before.

FIG. illustrates a modified form of the invention shown in FIG. 8 in which a flat cantilever bimetal element 200 is used with the electric heater 174 of FIG. 8, and the desired snap action is provided solely by mechanical means. In FIG. 10, elements common to those in FIGS. 1, 2, 3, 3a and 8 are indicateed by the like reference numerals. Referring to FIG. 10, diaphragm 136 is biased leftwardly by a spring 192 with sufiicient force to overpower the force of spring 53 (FIG. 2). Diaphragm 136 has secured thereto a latch or detent member 194 biased downwardly by a leaf spring 196 secured to a cover 198. The detent member includes a catch portion disposed to engage the end of the cantilever bimetal element 200, as shown, which is fixed at its other end. The detent member 194 also includes a cam portion disposed to engage a fixed cam 204. In operation, when the heater 174 (which is coiled around bimetal element 200) is energized the bimetal element engages the detent to overpower spring 192 and move the diaphragm 136 and detent to the right. After a predetermined travel, the detent strikes cam 204 and is lifted free of the bimetal element so that spring 192 snaps diaphragm 136 and detent 194 to the left which initiates unit only when frost has formed on coil 30, as described above. The rest of the operation is the same as described for FIG. 8. When the heater 174 is de-energized, the bimetal element 200 slowly moves to its inactive dotted position to again engage the latch projection of detent 194.

FIG. 10a illustrates a modification of the form of my invention shown in FIG. 10 in that a bellows 286 is sealed and filled with a gas such as air or nitrogen to expand when heated by the electric heater 174 inside the bellows and controlled by the thermostat 58. An arm 208 which is hinged at one end to a fixed support replaces the bimetal element 260 but engages the projection of latch detent 194. The construction otherwise operates in the same manner as the apparatus shown in FIG. 10, such that when the heater 174 is energized, the bellows expands to carry arm 2G8, detent 194 and diaphragm 136 to the right until release of the detent is effected by cam 204. If desired, belows 266 may actuate diaphragm 136 directly, or replace diaphragm 136.

The apparatus shown in FIGS. 11 and Ila is similar to the apparatus shown in FIGS. 9 and 10a except that a force-amplifying mechanism, such as a ratchet and cam mechanism, is interposed between the actuating element and diaphragm 136 in order to reduce the required size and force of such actuating element as well as reducing the source energy required. Broadly, this reduction in the size of the actuating element and the energy required therefor is to provide such a force-amplifying mechanism which integrates and stores the small energy over an extended period of time; and means are provided to release this stored energy at the end of this time period to provide a substantially larger actuating force than possible without the integrating mechanism.

Referring to FIG. 11, elements common to previous figures are indicated by like reference numerals, and the electric circuit is the same as illustrated in FIG. 8. In FIG. 11, the cantilever bimetal element 200 comprises the actuating or power element; this bimetal element is fixed at one end to support 202 and is free at its other end to move from a stop 210 to a stop 212 as electric heat energy is intermittently applied by a coil 174, controlled by the thermostat 58 in the form shown. The integrating mechanism includes the following elements: A ratchet arm 214, which is hinged to the free end of bimetal strip 200 and biased downwardly by a spring 216 is moved by the bimetal 203 to engage and move one tooth 218 of a ratchet wheel 220. Reverse rotation of the wheel is prevented by a leaf spring pawl 222 secured to a fixed support 224. A spiral shaped cam 226 having a step 227 is operatively connected to wheel 220 for rotation therewith by shaft means 228, which is journaled by any suitable bushing means 230. A lever arm 232 is fulcrumed at a support 234 and actuates diaphragm 136 through a shaft 236. The integrated energy of the small bimetal 200 is stored in a spring 238 which acts on lever 232 with a force that can always overpower the force of spring 53 (FIG. 2) and causes the upper end of the lever to ride on the surface of cam 226.

The device shown in FIG. 11 operates as follows: In the form shown, each normal compressor cycle causes a small wattage to energize heater 174 to revolve the ratchet wheel one tooth-length. After a number of compressor cycles (or equivalent intermittent energizing of heater 174) corresponding to one less than the number of teeth of wheel 220, the cam 226 arrives at the position shown. At the next energization of heater 174, as produced in the example shown by the next compressor cycle, spring 238 causes the end of lever 232 to snap over step 227 to the smallest radius of cam 226 to release the energy stored in spring 238 by intermittent heater 174. This action enables the actuator elements, 232, 236 and 136 to provide a large intermittent force to initiate the defrost action when called for. In the form shown, the lever 232 snaps diaphragm 136 to the left, thereby converting the spring energy to pressure energy which initiates unit 15 to defrost only when sufiicient frost has formed on tube 30, all in a manner described above. FIG. 11a shows merely that the ratchet 220 can be actuated by the solenoid shown in FIG. 9 which is operated-at each compressor cycle instead of the bimetal and heater illustrated in FIG. 11. A spring 24% biases armature 184 leftwardly, but the rest of the operation of the form shown in FIG. 11a is the same as for FIG. 11. The advantage of this integrating mechanism is that the required size of the bimetal element 204] and heater element 174, as well as the source of energy therefor, can be reduced somewhat inversely as the number of teeth of ratchet 220. This is true since spring 238 can be charged or cocked in eight steps (as illustrated), for example, instead of one step as for the form of FIG. 9 or 10.

Having now described my invention, it is important to appreciate that the defrosting control system disclosed herein for domestic refrigerators may be applied equally well to control ice thickness in commercial refrigeration, air conditioning, heat pumps, soft drink coolers or any other device for sensing and controlling the formation and/or melting of ice. Also the control invention has been illustrated using air pressure to actuate the diaphragm 10 2; but the inventive concepts would be unchanged if any fluid under pressure or vacuum were used in the fluid circuit by reversing or rearranging the diaphragm and its associated circuit.

In its broadest aspect, the control device of the present invention can be used in any application in which any substantially firm or solid material is subjected to a change in shape such as in its size, height, depth, thickness, etc., of its bulk or mass, and in which device means are provided to sense such change in shape (or to detect the presence or absence of such mass or body) to control the bulk of said material to any predetermined value. In those instances in which a mass is in one place at one time but is not present at another time, such changes can also be sensed by the control device of the present invention. Other uses and modifications of the invention may be made without departing from the spirit and scope of the appended claims.

What I claim is:

1. In a device to control an operating condition of a refrigerating machine in accordance with the formation of ice on a surface therein, the combination of; control means to effect a change in said operating condition, an

air circuit including means to produce an air pressure therein, movable pressure responsive means communicating with said circuit and being operatively connected to said control means for actuation thereof in response to a change in said circuit pressure, sensing means to detect the formation and melting of ice Within said refrigerating machine and including a portion for enabling said air pressure to escape and dissipate from said circuit to the atmosphere prior to the formation of a predetermined thickness of said ice, whereby said pressure responsive means is not operable, and said sensing means being disposed to contain said air pressure in said circuit after said predetermined thickness of ice is formed to enable said movement of said pressure responsive means for actuating said control means, said sensing means including conduit means communicating with said circuit, and said sensing portion comprising an open end of said conduit means mounted at a predetermined distance from said surface and adapted to be covered by said ice when it forms to said thickness corresponding at least to said distance to seal said open end from the atmosphere.

2. In a control device associated with apparatus having a surface subject to the formation of frozen substance adjacent thereto, the combination of; means to control the amount of said frozen substance, actuating means movable completely independent of said control means during one thickness condition of said substance but adapted to operate said control means during a second thickness condition of said substance, sensing means including an aperture mounted at a predetermined distance from said surface and dependent on the formation of said frozen substance and operatively associated with a fluid medium movable in response to movement of said actuating means to preclude said actuating means from operating said control means at least in said first-named condition when said formation of said frozen substance is less than a predetermined amount, said sensing means aperture being sulficiently covered by said frozen substance at said second condition thereof for enabling said actuating means to be operatively connected to said control means for operation thereof after said frozen substance has formed to substantially said predetermined amount.

3. In a control device associated with apparatus having a surface subject to the formation of a meltable and freezable material adjacent thereto, the combination of; means to control the thickness of said material forming on said surface, actuating means movable periodically completely independent of said control means during one thickness condition of said material but adapted to operate said control means during a second thickness condition of said material, sensing means including an aperture to measure the thickness of said material and mounted at a predetermined distance from said surface corresponding to said thickness, a working fluid operatively associated with said sensing means and movable in response and corresponding to said periodic movements in said first-named condition whenever said material has formed less than said predetermined thickness thereon, said movements of said working fiuid being substantially prevented by the bulk of said material upon formation thereof to said predetermined thickness to cover said aperture in said secondnamed thickness condition to enable actuation of said control means by said actuating means.

References Cited UNITED STATES PATENTS 1,742,062 12/1929 Day 62-155 X 1,999,191 4/1935 Hirschl 62-156 2,007,409 7/1935 Schweitzer 62-128 X 2,064,396 12/1936 Vo lpin 62-153 2,066,235 12/1936 Smilak 62-208 X 2,187,258 1/1940 Wood 62-227 X 2,255,179 9/1941 McIntosh 236-79 2,595,967 5/1952 McCloy 62-153 X 2,624,180 1/1953 Grimshaw 62-140 2,704,441 3/1955 Morton 62-140 2,744,389 5/1956 Raney 62-140 2,770,952 11/1956 Judd 62-153 2,867,092 l/1959 Perry a- 62-153 X 2,949,016 8/1960 Thorner 62-153 2,957,316 10/1960 Buchanan 62-153 ROBERT A. OLEARY, Primary Examiner. R. E. BACKUS, W. E. WAYNER, Assistant Examiners. 

2. IN A CONTROL DEVICE ASSOCIATED WITH APPARATUS HAVING A SURFACE SUBJECT TO THE FORMATION OF FROZEN SUBSTANCE ADJACENT THERETO, THE COMBINATION OF ; MEANS TO CONTROL THE AMOUNT OF SAID FROZEN SUBSTANCE, ACTUATING MEANS MOVABLE COMPLETELY INDEPENDENT OF SAID CONTROL MEANS DURING ONE THICKNESS CONDITION OF SAID SUBSTANCE BUT ADAPTED TO OPERATE SAID CONTROL MEANS DURING A SECOND THICKNESS CONDITION OF SAID SUBSTANCE, SENSING MEANS INCLUDING AN APERTURE MOUNTED AT A PREDETERMINED DISTANCE FROM SAID SURFACE AND DEPENDENT ON THE FORMATION OF SAID FROZEN SUBSTANCE AND OPEATIVELY ASSOCIATED WITH A FLUID MEDIUM MOVABLE IN RESPONSE TO MOVEMENT OF SAID ACTUATING MEANS TO PRECLUDE SAID ACTUATING MEANS FROM OPERATING SAID CONTROL MEANS AT LEAST IN SAID FIRST-NAMED CONDITION WHEN SAID FORMATION OF SAID FROZEN SUBSTANCE IS LESS THAN A PREDETERMINED AMOUNT, SAID SENSING MEANS APERTURE BEING SUFFICIENTLY COVERED BY SAID FROZEN SUBSTANCE AT SAID SECOND CONDITION THEREOF FOR ENABLING SAID ACTUATING MEANS TO BE OPERATIVELY CONNECTED TO SAID CONTROL MEANS FOR OPERATION THEREOF AFTER SAID FROZEN SUBSTANCE HAS FORMED TO SUBSTANTIALLY SAID PREDETERMINED AMOUNT. 